October 11, 2012

WEST LAFAYETTE, Ind. - Farmers should consider the short-
and long-term effects of fall tillage on their fields and not just the effects
of the drought on this year's crop, a Purdue Extension
agronomist says.

Tillage loosens and rearranges soil aggregates with the
intent of establishing a better foundation for crop seed placement and root
growth, but the drought itself has already accomplished deep cracking and
loosening of some soils. The drought also reduced the post-harvest crop residue
that is often used as an additional justification for tillage.

"Tillage decisions should never be based on one
year's crop yield," Tony Vyn said.

A farmer's natural reaction to a drought year is
disappointment, and that may lead to what Vyn called "revenge
tillage."

"I don't want farmers to overestimate the need for
fall tillage just because of the 2012 drought and poor crops," he said.
"It's important to adopt a tillage system that leaves topsoil uniformly in
place to build up a whole field's resiliency in root-zone water retention over
time."

He urged farmers to exercise caution and always be aware
of the soil loss risk, saying they should examine soil conditions and crop
yields over a number of years when considering tillage.

"The early harvest may promote fall tillage, and the
disappointment factor may further motivate farmers to till ground," Vyn
said. "But often we don't know how an individual year's yields would have
changed with more or less tillage.

"It's been consistent that there are very few
yield-related reasons for doing fall tillage on well-drained soils in a
corn-soybean rotation. There's more justification when a field is on a
corn-corn rotation or it has poorly drained soils. "

In addition to considering tillage in fields on a
corn-corn rotation, Vyn recommended that farmers consider limited fall tillage
for fields with a history of compaction, high clay content, lack of systematic
drainage or fields with very slow-drying soils.

He also advised farmers to consider the risks of fall
tillage on their fields, especially in sloped areas. They should consider the
amount of topsoil that could be lost, and the future yield loss in those eroded
areas, if they bury residue that could be left to provide protection from
runoff.

"Tillage has a permanent effect that can forever
change soil water-holding capability on slopes," Vyn said.

Normally, the protective residue cover and greatly reduced
soil disturbance associated with no-till mean less evaporation loss and higher
soil water availability to roots. But this year, no-till fields did not provide
as much protection against the drought as expected.

The early-season onset of high temperatures and lack of rain
limited both root growth and shoot growth in 2012. Corn and soybean varieties
differ in their relative rooting ability under stress conditions, but rooting
in all varieties after the early seedling stage depends on energy reserves
coming from shoot growth.

"The near-surface soil was so dry, lack of tillage
meant more resistance to root penetration, meaning corn or soybean plants in
those fields sometimes experienced more drought stress before flowering than
other tilled fields, despite the crop residue cover," Vyn said. "But
we may never see such a severe, early drought occur with that combination of
timing and high temperatures again.

If farmers decide to practice fall tillage, they can
choose from several management techniques. Standard primary tillage procedures
include using a disk, chisel plow, deep ripper, moldboard plow or strip tiller.

Vyn said agronomists favor strip tillage because it allows
for minimal soil mixing and residue incorporation while preparing fields for
earlier seeding of spring crops, and it can be combined with fertilizer
application.

"It's a proven, versatile tillage practice that
creates a warmer, drier zone of soil in the spring that ensures timely seed
placement in both corn-soybean and corn-corn rotations," Vyn said.
"Precision automatic guidance systems have also simplified crop row
placement in the center of the loosened strips."

He said there's still time yet for farmers to decide whether
fall tillage is needed for their fields and that they shouldn't rush the
decision. With fall rains, farmers should be cautious and not rush fall tillage
on soils that may be too wet.